Spacers for packaged microelectronic imagers and methods of making and using spacers for wafer-level packaging of imagers

ABSTRACT

Methods of packaging microelectronic imagers and packaged microelectronic imagers. An embodiment of such a method can include providing an imager workpiece having a plurality of imager dies arranged in a die pattern and providing a cover substrate through which a desired radiation can propagate. The imager dies include image sensors and integrated circuitry coupled to the image sensors. The method further includes providing a spacer having a web that includes an adhesive and has openings arranged to be aligned with the image sensors. For example, the web can be a film having an adhesive coating, or the web itself can be a layer of adhesive. The method continues by assembling the imager workpiece with the cover substrate such that (a) the spacer is between the imager workpiece and the cover substrate, and (b) the openings are aligned with the image sensors. The attached web is not cured after the imager workpiece and the cover substrate have both been adhered to the web. As such, the web does not outgas contaminants into the compartments in which the image sensors are housed.

TECHNICAL FIELD

The methods and devices described below are related to packagingmicroelectronic imagers having solid state image sensors. Morespecifically, several embodiments of the invention are related towafer-level packaging of microelectronic imagers by attaching an imagerworkpiece on one side of a prefabricated spacer and attaching a coversubstrate on an opposing side of the spacer.

BACKGROUND

Microelectronic imagers are used in digital cameras, wireless deviceswith picture capabilities, and many other applications. Cell phones andPersonal Digital Assistants (PDAs), for example, are incorporatingmicroelectronic imagers for capturing and sending pictures. The growthrate of microelectronic imagers has been steadily increasing as theybecome smaller and produce better images with higher pixel counts.

Microelectronic imagers include image sensors that use Charged CoupledDevice (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS)systems, or other solid state systems. CCD image sensors have beenwidely used in digital cameras and other applications. CMOS imagesensors are also quickly becoming very popular because they are expectedto have low production costs, high yields and small sizes. CMOS imagesensors can provide these advantages because they are manufactured usingtechnology and equipment developed for fabricating semiconductordevices. CMOS image sensors, as well as CCD image sensors, areaccordingly “packaged” to protect the delicate components and to provideexternal electrical contacts.

FIG. 1 is a schematic view of a conventional microelectronic imager 1with a conventional package. The imager 1 includes a die 10, aninterposer substrate 20 attached to the die 10, and a spacer 30 attachedto the interposer substrate 20. The spacer 30 surrounds the periphery ofthe die 10 and has an opening 32. The imager 1 also includes atransparent cover 40 over the die 10.

The die 10 includes an image sensor 12 and a plurality of bond-pads 14electrically coupled to the image sensor 12. The interposer substrate 20is typically a dielectric fixture having a plurality of bond-pads 22, aplurality of ball-pads 24, and traces 26 electrically coupling bond-pads22 to corresponding ball-pads 24. The ball-pads 24 are arranged in anarray for surface mounting the imager 1 to a board or module of anotherdevice. The bond-pads 14 on the die 10 are electrically coupled to thebond-pads 22 on the interposer substrate 20 by wire-bonds 28 to provideelectrical pathways between the bond-pads 14 and the ball-pads 24.

The imager 1 shown in FIG. 1 also has an optics unit including a support50 attached to the transparent cover 40 and a barrel 60 adjustablyattached to the support 50. The support 50 can include internal threads52, and the barrel 60 can include external threads 62 engaged with thethreads 52. The optics unit also includes a lens 70 carried by thebarrel 60.

One aspect of fabricating the imager 1 is forming the spacer 30 andattaching the cover 40 to the spacer 30. The spacer 30 can be formed byplacing an uncured, flowable epoxy onto the interposer substrate 20. Ina typical application, the interposer substrate 20 has a plurality ofseparate dies 10, and the spacer 30 is formed as a grid of uncured epoxyon the interposer substrate 20 in the areas between adjacent dies 10.After depositing the epoxy, the cover 40 is attached to the spacer 30.The epoxy is then cured to harden the spacer 30 such that it becomesdimensionally stable after enclosing the die 10 between the cover 40 andthe interposer substrate 20.

One problem of forming the spacer 30 by stenciling an uncured epoxy onthe interposer substrate is that the stenciling process produces atextured surface on the top surface of the spacer 30. This can lead toleaks between the spacer 30 and the cover 40 through which moisture orother contaminants can enter into the cavity where the image sensor 12is located. Another problem of forming the spacer 30 by stenciling anuncured epoxy onto the substrate is that the height of the spacer 30 islimited because the epoxy tends to slump after the stencil is removed.This causes the epoxy to flow laterally and occupy a significantpercentage of the real estate on the substrate 20. Additionally, asignificant problem of using an uncured epoxy is that the uncured epoxyoutgases during the curing cycle after the cover is mounted to theepoxy. Such outgasing can contaminate the compartment and impair or ruinthe performance of the die 10.

Another process for forming the spacer 30 is to dispense a small flow ofuncured epoxy via a needle-like tube or nozzle between adjacent dies.This process is undesirable because it is difficult to control the flowof the uncured epoxy at the intersections of the grid. The intersectionstypically have rounded corners that occupy additional real estate on theinterposer substrate. Additionally, as with the stencil printingprocess, the epoxy is cured after the cover 40 is mounted to the spacer30 such that it outgases into the image sensor compartment. Therefore,processes that dispense an epoxy using needle-like tubes are alsoundesirable.

U.S. Pat. No. 6,285,064 discloses another process in which a preformedadhesive matrix is fabricated in the shape of a wafer. The adhesivematrix has openings in the pattern of the image sensors, and it isformed separately from the wafer. In operation, the adhesive matrix isattached to the wafer such that the openings are aligned with themicrolenses, and a cover glass is then attached to the top of theadhesive matrix. The adhesive matrix is subsequently activated byapplication of light, pressure and/or heat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a packaged microelectronic imager inaccordance with the prior art.

FIG. 2 is an exploded cross-sectional isometric view of an imagerassembly having a plurality of microelectronic imagers that have beenpackaged at the wafer level in accordance with an embodiment of theinvention.

FIG. 3 is a cross-sectional view taken along line A-A of FIG. 2illustrating a portion of a spacer for use in wafer-level packaging ofmicroelectronic imagers in accordance with an embodiment of theinvention.

FIG. 4 is a cross-sectional view illustrating a plurality ofmicroelectronic imagers that have been packaged with the spacer shown inFIG. 3 in accordance with an embodiment of the invention.

FIG. 5 is a cross-sectional view illustrating a portion of a spacer foruse in packaging microelectronic imagers in accordance with anotherembodiment of the invention.

FIGS. 6A-6C are cross-sectional views illustrating a method ofwafer-level packaging of microelectronic imagers in accordance withadditional embodiments of the invention.

FIGS. 7A and 7B are isometric views illustrating different embodimentsof spacers on imaging workpieces in accordance with the invention.

DETAILED DESCRIPTION

A. Overview

The following disclosure describes several embodiments of (1) spacersfor use in wafer-level packaging of microelectronic imagers, (2)microelectronic imagers including such spacers, (3) methods forwafer-level packaging of microelectronic imagers, and (4) methods forproducing or otherwise providing prefabricated spacers for use inmicroelectronic imagers. Wafer-level packaging of microelectronicimagers is expected to significantly enhance the efficiency ofmanufacturing imaging devices because a plurality of imagers can bepackaged simultaneously using highly accurate and efficient processesdeveloped for packaging semiconductor devices. Wafer-level packaging ofmicroelectronic imagers is also expected to enhance the quality andperformance of such imagers because the semiconductor fabricationprocesses can reliably produce and assemble the various components witha high degree of precision. As such, several embodiments of wafer-levelpackaging processes for packaging microelectronic imagers and theimagers packaged using such processes disclosed herein are expected tosignificantly reduce the cost for assembling microelectronic imagers,increase the performance of imaging devices, produce smaller imagerscompared to conventional devices, and produce higher quality imagers.

One aspect of the invention is directed toward methods of packagingmicroelectronic imagers. An embodiment of such a method can includeproviding an imager workpiece having a plurality of imager dies arrangedin a die pattern and providing a cover substrate through which a desiredradiation can propagate. The imager dies include image sensors andintegrated circuitry coupled to the image sensors. The method furtherincludes providing a spacer having a web that includes an adhesive andhas openings arranged to be aligned with the image sensors. For example,the web can be a film having an adhesive coating, or the web itself canbe a layer of adhesive. The method continues by assembling the imagerworkpiece with the cover substrate such that (a) the spacer is betweenthe imager workpiece and the cover substrate, and (b) the openings arealigned with the image sensors. The attached web is not cured after theimager workpiece and the cover substrate have both been adhered to theweb. As such, the web does not outgas contaminants into the compartmentsin which the image sensors are housed.

Another embodiment of a method for packaging a plurality of imager diesincludes forming a spacer having a web including an adhesive and aplurality of openings arranged in a die pattern corresponding to thepattern of individual imager dies on an imager workpiece. Thisembodiment further includes (a) adhering the imager workpiece to oneside of the spacer with the image sensors being aligned with theopenings, and (b) adhering a cover substrate to an opposite side of thespacer such that the image sensors are enclosed in individualcompartments within the openings in the web. In this embodiment, the webis not cured after the imager workpiece and the cover substrate haveboth been adhered to the spacer.

Still another embodiment of a method in accordance with the invention isdirected toward assembling an imager workpiece having a plurality ofimager dies arranged in a die pattern with an optically transmissivecover substrate. The individual imager dies include an image sensor andan integrated circuit operatively coupled to the image sensor. Thisembodiment comprises prefabricating a spacer having a web with a desiredthickness to space the imager workpiece apart from the cover substrateby a desired distance, openings arranged in the die pattern, asubstantially flat first side, and a substantially flat second side. Theweb is in a non-flowable state before enclosing the image sensor betweenthe imager workpiece and the cover substrate. This method furtherincludes sealing (a) the imager workpiece to the first side of the websuch that individual image sensors are aligned with a correspondingopening in the web, and (b) sealing the cover substrate to the secondside of the web opposite the first side to enclose the image sensorsbetween the imager workpiece and the cover substrate.

Another aspect of the invention is directed toward producing a spacerfor separating the imager workpiece from the cover substrate by desireddistance. This method comprises producing a non-flowable film having afirst flat surface and a second flat surface spaced apart from the firstflat surface by a thickness at least approximately equal to the desireddistance between the imager workpiece and the cover substrate. Themethod continues by forming holes in the non-flowable film in the diepattern. The method can further include coating the film with anadhesive.

Additional aspects of the invention are directed toward microelectronicimager assemblies. In one embodiment, a microelectronic imager assemblycomprises an imager workpiece having a plurality of imager dies arrangedin a die pattern and a cover substrate. The individual imager diesinclude an image sensor and an integrated circuit operatively coupled tothe image sensor. The cover substrate can be an optically transmissiveplate, or it can be transmissive to another type of radiation in anoperating spectrum of the image sensors. The imager assembly furtherincludes a spacer. In one embodiment, the spacer has an integral webwith a first side adhered to the workpiece, a second side spaced apartfrom the first side by a prefabricated separation distance and adheredto the cover substrate, and openings arranged in the die pattern andaligned with corresponding image sensors. This embodiment of the webincludes a material in a cured, non-flowable state before the imagerworkpiece and the cover substrate are both adhered to the spacer. Inanother embodiment, the spacer is a prefabricated web including aplurality of cut-edged openings arranged in the die pattern and alignedwith the image sensors. The web further includes a first side adhered tothe imager workpiece, a second side adhered to the cover substrate, anda thickness that spaces the image sensors apart from the cover substrateby a desired distance.

Specific details of several embodiments of the invention are describedbelow with reference to CMOS imagers to provide a thorough understandingof these embodiments, but other embodiments can use CCD imagers or othertypes of solid state imaging devices. Several details describingstructures or processes that are well known and often associated withother types of microelectronic devices are not set forth in thefollowing description for purposes of brevity. Moreover, although thefollowing disclosure sets forth several embodiments of different aspectsof the invention, several other embodiments of the invention can havedifferent configurations or different components than those described inthis section. As such, it should be understood that the invention mayhave other embodiments with additional elements or without several ofthe elements described below with reference to FIGS. 2-7B.

B. Wafer-Level Packaged Microelectronic Imagers

FIG. 2 is an exploded, cross-sectional isometric view of an imagerassembly 200 in accordance with an embodiment of the invention. In thisembodiment, the imager assembly includes an imager workpiece 202, aspacer 204, and a cover substrate 206. The imager workpiece 202 includesa first substrate 210, a plurality of imager dies 211 having imagesensors 212 arranged in a die pattern on the first substrate 210, andlanes 214 between the image sensors 212. The spacer 204 includes a web220 having a first side 222, a second side 224, and a plurality ofopenings 226. The first side 222 is spaced apart from the second side224 by a thickness “T” at least approximately equal to a desiredseparation distance between the imager workpiece 202 and the coversubstrate 206. The openings 226 are arranged in the die pattern so thatthe image sensors 212 are aligned with corresponding openings 226. Thecover substrate 206 is a plate composed of a material through which adesired radiation for the image sensor 212 can propagate. The coversubstrate 206, for example, can be quartz, glass, or another type ofoptically transparent material. The cover substrate 206 is generally asecond substrate having the same or similar shape as the first substrate210. Additionally, the cover substrate 206 is adhered to the second side224 of the web 220 to enclose the image sensors 212 in correspondingcompartments defined by the openings 226.

The web 220 of the spacer can be a prefabricated unit that isconstructed separately from the imager workpiece 202 and the coversubstrate 206, or the web 220 can be constructed on one of the imagerworkpiece or cover substrate 206. The web 220 is composed of a materialthat is not cured after the imager workpiece and the cover substratehave both been adhered to the spacer. As such, the spacer 204 is adimensionally stable component with precise dimensions.

The imager assembly 200 illustrated in FIG. 2 is expected to provideseveral advantages compared to conventional imaging assemblies havingconventional spacers, as shown above with reference to FIG. 1. Forexample, because the web 220 is not cured after the imager workpiece 202and the cover substrate 206 have both been adhered to the spacer 204,the web 220 does not outgas contaminants into the openings 226 after theimage sensors 212 have been fully enclosed. Additionally, the spacer 204can be composed of a substantially incompressible material and theopenings 226 can be cut into the web 220 such that the spacer 204 has acontrolled thickness and the openings 226 have well-defined “cut-edge”sidewalls 228. The spacer 204 accordingly provides a dimensionallystable and highly accurate interface between the imager workpiece 202and the cover substrate 206. Moreover, the second side 226 of the web220 can be highly planar such that it provides an extremely good sealwith the cover substrate 206 to avoid leaks. FIGS. 3-7B illustrateseveral specific embodiments of spacers that provide several of theseadvantages and additional benefits as set forth below.

C. Embodiments of Spacers for Wafer-Level Packaging of MicroelectronicImagers

FIG. 3 is a cross-sectional view illustrating a portion of oneembodiment of the spacer 204. In this embodiment, the web 220 includes afilm 310 having a first side 312 and a second side 314. The web 220further includes a first adhesive 322 on the first side 312 of the film310, and a second adhesive 324 on the second side 314 of the film 310.The embodiment of the spacer 204 illustrated in FIG. 3 further includesa first release element 332 over the first adhesive 322 and a secondrelease element 334 over the second adhesive 324. The first and secondrelease elements 332 and 334 can be peeled away from the first andsecond adhesives 322 and 324, respectively, to expose the adhesivesbefore attaching the imager workpiece 202 (FIG. 2) and the coversubstrate 206 (FIG. 2) to the spacer 204.

The embodiment of the spacer 204 shown in FIG. 3 can be fabricated bycoating a sheet of the film 310 with the first and second adhesives 322and 324, and subsequently applying the release elements 332 and 334 tothe first and second adhesives 322 and 324. In another embodiment, thefirst and second adhesives 322 and 324 can be applied to the first andsecond release elements 332 and 334, respectively, and then the assemblyof the adhesives and release elements can be rolled onto a sheet of thefilm 310. The spacer 204 can then be completed by forming the openings226. The openings 226 are generally cut through the release elements,adhesives and the film to form cut edges 340 along the sidewalls 228.The holes 226 can be cut using a punch/die stamp, a knife-edged stamp orroller, lasers and/or water jets.

The film 310 and the adhesives 322 and 324 can be made from severaldifferent materials. In one embodiment, the film 310 is a tape that iseither in a precured or post-cured state. Suitable tapes includepolyimide films, polyester films, ultra-high molecular weight films,PTFE films, and other suitable materials. Such materials are readilyavailable from Tapes II International located in Santa Ana, Calif. Theadhesives can be any suitable adhesives used in the semiconductorpackaging industry or elsewhere.

FIG. 4 is a cross-sectional view illustrating a portion of the imagerassembly 200 after the imager workpiece 202 and the cover substrate 206have been adhered to the spacer 204. The imager assembly 200 includes aplurality of individual imagers 400 that have an imaging die 211 alignedwith an opening 226 in the spacer 204. In this embodiment, individualimaging dies 211 include an image sensor 212, an integrated circuit 410operatively coupled to the image sensor 212, and external contacts 420operatively coupled to the integrated circuit 410. The external contacts420 illustrated in FIG. 4 are through-wafer interconnects havingexternal contacts pad 422 at the backside of the first substrate 210.

The imager assembly 200 is assembled by removing the first releaseelement 332 from the first adhesive 322 and aligning the openings 226with corresponding image sensors 212. The first adhesive 322 is thenadhered to the imager workpiece 202. The second release element 334 issubsequently removed from the second adhesive 324, and the coversubstrate 206 is adhered to the second adhesive 324. This process can bereversed such that the second side 314 of the film 310 is adhered to thecover substrate 206 before the first side 312 of the film 310 is adheredto the imager workpiece 202.

The imager assembly 200 is constructed by assembling the imagerworkpiece 202 and the cover substrate 206 with the web 310 after the web310 is in a state that does not require subsequent curing. The web 310,therefore, is not cured after the imager workpiece 202 and the coversubstrate 206 have both been adhered to the spacer 204 and the imagesensors 212 have been enclosed in the openings 226. As such, the web 310is incompressible and/or in an otherwise non-flowable state when theimager workpiece 202 and the cover substrate 206 are both adhered to thespacer 204.

The imager assembly 200 is expected to provide several benefits comparedto conventional processes and devices for spacing the cover apart fromthe image sensors. First, because the web 310 is not cured after sealingthe imager workpiece 202 and the cover substrate 206 to the web 310, thespacer 204 does not significantly outgas into the openings 226 enclosingthe image sensors 212. This is expected to significantly reduce thecontaminants and enhance the quality of the imagers 400. The spacer 204is also dimensionally stable when the imager workpiece 202 and the coversubstrate 206 are attached to the spacer 204. This is expected toprovide highly accurate spacing between the imager workpiece 202 and thecover substrate 206. Moreover, cutting the web 310 to form the openingsis a relatively inexpensive process.

FIG. 5 is a cross-sectional view illustrating another embodiment of thecover 204 that can be used in an imager assembly. In this embodiment,the cover 204 includes a film 510 and a backing 520 that carries thefilm 510. The film 510 is an adhesive with a first side 512 and a secondside 514 spaced apart from the first side 512 by a distanceapproximately equal to the desired spacing between the imager workpiece202 and the cover substrate 206. The film 510 is either formed on thebacking 520 by depositing a layer of adhesive in a flowable state andthen curing the adhesive before presenting the spacer 204 to the imagerworkpiece 202. Alternatively, the film 510 can be formed in a moldingprocedure separately from the backing 520 and then attached to thebacking 520. The openings 226 can be formed in the film 510 using astamping or cutting procedure as described above with reference to FIG.3, or the openings 226 can be molded.

The embodiment of the cover 204 illustrated in FIG. 5 can be assembledwith the imager workpiece 202 (FIG. 2) and the cover substrate 206 (FIG.2) by attaching the first side 512 of the web 510 to the imagerworkpiece 202 such that the openings 226 are aligned with the imagesensors 212 (FIG. 4). The backing 520 is then removed from the secondside 514 of the web 510. The backing can be removed by peeling it fromthe web 510. For example, the web 510 can be composed of a UV-activatedmaterial that responds to ultraviolet radiation such that the backing520 can be removed from the second side 514 of the web 510. The coversubstrate 206 is attached to the second side 514 of the web 510 afterremoving the backing 520. Alternatively, the film 510 can be attached tothe cover substrate 206 first, and then the imager workpiece 202 can beattached to the other side of the film 510.

FIGS. 6A-6C are cross-sectional views illustrating sequential stages ofa method for producing a spacer on an imager assembly in accordance withanother embodiment of the invention. Referring to FIG. 6A, this processincludes covering the imager workpiece 202 with a layer of web material600. The web material 600 can be a photosensitive dry film adhesive or aliquid adhesive in a flowable state. In one embodiment, the adhesive caninclude photopatternable polydimethylsiloxane (PDMS) that can beactivated by an O₂ plasma. Other embodiments can use liquid or dryadhesives that can be rolled, sprayed or applied to the workpiece usingother techniques. After depositing the adhesive 600 onto the imagerworkpiece 202, the adhesive 600 is patterned using a mask 605 and anappropriate radiation R to cure the exposed portions of the adhesive600.

FIG. 6B illustrates a subsequent stage in the method at which a web 610is formed from the adhesive 600 by removing the unexposed portions ofthe adhesive 600 to create a plurality of openings 612 aligned with theimage sensors 212. The web 610 and openings 612 together define a spacer620. In the case of PDMS, the exposed upper surface of the web 610 isthen activated for adhesion using an O₂ plasma. Referring to FIG. 6C,the cover substrate 206 is then attached to the activated upper surfaceof the web 610 to enclose the image sensors 212 in the opening 612.

The method described above with reference to FIGS. 6A-6C can haveseveral different embodiments. For example, the method can furtherinclude cleaning the image sensors 212 after forming the openings 612 toremove any contaminants generated while forming the openings 612. Inanother embodiment, the adhesive 600 can be deposited onto the coversubstrate 206 and then the openings 612 can be formed in the adhesive600 to fabricate the spacer 620 on the cover substrate 206 instead ofthe imager workpiece 202. It follows that the bottom surface of the web610 can be activated using an appropriate plasma, and the imagerworkpiece 202 can be attached to the activated bottom surface of the web610.

FIGS. 7A and 7B illustrate different configurations of the spacers foruse in imager assemblies in accordance with additional embodiments ofthe invention. Referring to FIG. 7A, any of the spacers described abovecan be a grid 710 a having openings 712 aligned with image sensors (notshown in FIG. 7A) on the imager workpiece 202. Alternatively, FIG. 7Billustrates a different embodiment in which any of the spacers describedabove with reference to FIGS. 2-6C are defined by frames 710 bsurrounding individual image sensors 212 on the imager workpiece 202.The frames 710 b can be formed on a backing as described above withreference to FIG. 5 or a deposition/pattern process as described inFIGS. 6A-6B. Additionally, the frames 710 b can be formed on the coversubstrate instead of the imager workpiece 202. One aspect of the frames710 b is that the lanes between the image sensors 212 are not covered bythe spacers. This is expected to be advantageous for cutting the imagerworkpiece 202 because there is less material in the lanes between theimage sensors 212.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1.-37. (canceled)
 38. A microelectronic imager assembly, comprising: animager workpiece having a plurality of imager dies arranged in a diepattern, wherein individual imager dies include an image sensor and anintegrated circuit operatively coupled to the imager sensor; anoptically transmissive cover substrate; and a spacer having an integralweb with a first side adhered to the imager workpiece, a second sidespaced apart from the first side by a prefabricated separation distanceand adhered to the cover substrate, and openings arranged in the diepattern and aligned with corresponding image sensors, wherein the webincludes a material in a cured and non-flowable state before the imagerworkpiece and the cover substrate are both adhered to the spacer. 39.The imager assembly of claim 38 wherein the web comprises a filmcomposed of a tape, and the spacer further comprises a first layer ofadhesive on one side of the tape and a second layer of adhesive on anopposing side of the tape.
 40. The imager assembly of claim 38 whereinthe film comprises an adhesive formed and cured separately from theimager workpiece and the cover substrate, the film having cut-edgedopenings and a thickness at least approximately equal to the separationdistance.
 41. The imager assembly of claim 38 wherein the film comprisesa liquid adhesive deposited directly onto the imager workpiece in aflowable state and cured on the imager workpiece, wherein the adhesivehas a thickness at least approximately equal to the separation distanceand etched openings aligned with the image sensors.
 42. The imagerassembly of claim 38 wherein the film comprises a dry adhesive depositeddirectly onto the imager workpiece in an unactivated state andsubsequently activated on the imager workpiece, wherein the adhesive hasa thickness at least approximately equal to the separation distance andetched openings aligned with the image sensors.
 43. The imager assemblyof claim 38 wherein the film comprises a liquid adhesive depositeddirectly onto the cover substrate in a flowable state and cured on thecover substrate, wherein the adhesive has a thickness at leastapproximately equal to the separation distance and etched openingsarranged to be aligned with the image sensors.
 44. The imager assemblyof claim 38 wherein the film comprises a dry adhesive deposited directlyonto the cover substrate in an unactivated state and subsequentlyactivated on the cover substrate, wherein the adhesive has a thicknessat least approximately equal to the separation distance and etchedopenings arranged to be aligned with the image sensors.
 45. Amicroelectronic imager assembly, comprising: an imager workpiece havinga plurality of imager dies arranged in a die pattern, wherein individualimager dies include an imager sensor and an integrated circuitoperatively coupled to the image sensor; a cover substrate transmissiveto radiation in an operating spectrum of the image sensors; and aprefabricated spacer having a web including a plurality of cut-edgedopenings arranged in the die pattern and aligned with the image sensors,a first side adhered to the imager workpiece, a second side adhered tothe cover substrate, and a thickness that spaces the image sensors apartfrom the cover substrate by a desired distance.
 46. The imager assemblyof claim 45 wherein the web comprises a film composed of a tape, and thespacer further comprises a first layer of adhesive on one side of thetape and a second layer of adhesive on an opposing side of the tape. 47.The imager assembly of claim 45 wherein the web comprises an adhesiveformed and cured separately from the imager workpiece and the coversubstrate, the adhesive having the cut-edged openings and a thickness atleast approximately equal to the desired distance.
 48. The imagerassembly of claim 45 wherein the web comprises a liquid adhesivedeposited directly onto the imager workpiece in a flowable state andcured on the imager workpiece, wherein the adhesive has a thickness atleast approximately equal to the desired distance and etched openingsaligned with the image sensors.
 49. The imager assembly of claim 45wherein the web comprises a dry adhesive deposited directly onto theimager workpiece in an unactivated state and subsequently activated onthe imager workpiece, wherein the adhesive has a thickness at leastapproximately equal to the desired distance and etched openings alignedwith the image sensors.
 50. The imager assembly of claim 45 wherein theweb comprises a liquid adhesive deposited directly onto the coversubstrate in a flowable state and cured on the cover substrate, whereinthe adhesive has a thickness at least approximately equal to the desireddistance and etched openings arranged to be aligned with the imagesensors.
 51. The imager assembly of claim 45 wherein the web comprises adry adhesive deposited directly onto the cover substrate in anunactivated state and subsequently activated on the cover substrate,wherein the adhesive has a thickness at least approximately equal to thedesired distance and etched openings arranged to be aligned with theimage sensors.